I know I do not have functioning ABS, I've proved that on many occasions. I have an ABS light that does not come on, but I always assumed that was standard Dash issue, and just isn't ever powered in non-ABS cars.

Now two things have happened:
First, when replacing front end suspension, I noticed my front wheel assembly has teeth on it. I can only imagine that the teeth are for measuring how fast (or even if) a wheel is spinning. In other words, something for ABS.
The second thing that has come about, is I should replace my rear axle/CV joints. These are listed as w/ and w/o ABS, so it because important for me to know IF my car is supposed to have functioning ABS, even though it may not be functioning.

Does anyone have enough experience with these cars to know what to look for when figuring this info out?
The simplest method would be welcome ;-)

If your car has ABS then it will have brake lines running to a device in the front left area of the engine compartment just behind the headlights and below the cruise controller. If your car does have ABS then it will also have a computer just under the fog light switch behind the knee bolster. On top of that computer is a relay that protects the system from voltage spikes and is usually compromised from jumping a dead battery on the wrong terminals. This is most likely why the ABS would not work. There is also a light that is probably burned out in your dash or has been removed so that the car would pass inspection. I believe that all 1986 and newer US models were made with ABS. I could be wrong but 86 was the first year to have it.

Well son of a...
I've owned this car for 3 years and not known it had a (busted) ABS system? Hot damn
I checked next to the headlight, sure enough there is a metal device with metal brake lines going into it, with a bosch number that turns up an ABS part.

I'll have to check out the E30 ABS system now. I never bothered because I assumed my car didn't have it.
ABS would have been nice in the last 3 Spokane winters

QuoteEarendil
Well son of a...
I've owned this car for 3 years and not known it had a (busted) ABS system? Hot damn
I checked next to the headlight, sure enough there is a metal device with metal brake lines going into it, with a bosch number that turns up an ABS part.

I'll have to check out the E30 ABS system now. I never bothered because I assumed my car didn't have it.
ABS would have been nice in the last 3 Spokane winters

Thanks a lot for the help with that!

First place to look is at the ABS relay. Ferdinand may have some pictures that show the fuse that will need to be replaced.
Second will be the bulb in the cluster as it has probably been removed.

QuoteArcheo-peteriX
First place to look is at the ABS relay. Ferdinand may have some pictures that show the fuse that will need to be replaced.
Second will be the bulb in the cluster as it has probably been removed.

The Bentley says next to nothing about the ABS system, so that's a bummer. I have yet to do the regular google search, but if Ferd had pictures (or anyone else) that would be extremely helpful. The previous owner installed an alarm and keyless entry system, all of which have made for about a half million wires and extra boxes under the steering wheel a quick glance revealed nothing obvious that could be called an ABS system, and there wasn't a relay or fuse in sight.

So, likely causes are the fuse being blown, or the relay being bad? I have a spare cluster so I should be able to pop a new bulb in the ABS spot and see what lights up.

The bulb that goes in the cluster for the ABS is not like all the other ones as it has two wires that connect to a housing that holds the bulb. It is identical to the bulb that lights up the rear ashtray FYI. I also might have the correct relay for your ABS as I have one from my parts car. I would just have to check and see if the MY 91 is the same PN as your MY PN. I also have the ABS computer if that ends up being the problem.

One of the things I remember the best of driving my iX, it is the ABS. Though that one is differently programmed (high grip and low grip) than a RWD E30 (though the high grip part might be the same as a RWD), it must have been amoungst the best of its time. Very effective!

Okay, new bulb is in the cluster, and sure enough, the ABS lights up and won't go away

So I went looking around the steering column where I thought the ABS relay was supposed to be, and couldn't find anything. I spent 5 minutes upside down with my feet over the drivers head rest and my head on the floor boards trying to make sense of the wiring down there, which is only made worse by the remote/alarm alarm system.

Does anyone remember the color of the relay? How many wires go into it? General size? Any clue would be helpful.
I followed the thick set of wires coming out of the ABS computer, but lost track of it as it disappears up into the dash.
The relay isn't in the Bentley, so I'm at a bit of a loss

Thanks again, I found the relay right where you said it was.
So I took the relay out, opened it up, and found a broken wire. A little solder later, and it was read to be put back in the car.
With fingered crossed, I held the relay in one hand as I turned the key, in the "start" position (but car off), I could feel the relay click on, yay!
After starting the car however, the anti-lock brake light did not turn off
I found one normal fuse up on top of the ABS CPU, which looked good.

So, any ideas how to trouble shoot this, or can I just about assume it's the ABS computer?

Perhaps it's a wheel sensor as well? Any ideas what to look for there? Again, the Bentley says nothing but "Take to BMW Dealer" under the ABS section, and is completely unhelpful in diagnosing "normality" in this system.

Thanks once again for your help so far

~Tyler

(PS, why is this message marked as spam and in need of moderator approval?!)

QuoteEarendil(PS, why is this message marked as spam and in need of moderator approval?!)

I have no idea. That has happened with 3 or 4 messages since the forum was restarted, but I'll be damned if I can see anything in the messages that causes it. It seems to be completely random. I hate that -- it makes troubleshooting it a nightmare.

QuoteEarendilSo, any ideas how to trouble shoot this, or can I just about assume it's the ABS computer?

Check the wiring to the wheel sensors first. Each sensor has two wires encased in a rubber sheath. The wires leading to the front wheels tend to get beat up and cracked.

You can unplug the front ABS sensors at the connectors on the inner fenders in the engine compartment, check right next to the main, fuel pump, and O2 sensor relay box. From that unplugged connector, using a multitester, check the resistance of the ABS sensor. It should be close to zero resistance. Wiggle the cable to check for intermittent breaks in the wire, i.e. infinite resistance.

The sensors themselves need occasional cleaning. The sensor is a magnet with a coil winding around it. The tip of the magnet sits close to the toothed ABS ring. As each tooth or trough passes the tip of the magnet, it sets up a reversing voltage in the sensor coil which is then counted by the ABS controller.

The gap between the tip of the magnet and the toothed ring is critical. Because it is a magnet, it tends to collect bits of "stuff" on it's tip. Undo the bolt holding the sensor, pull it out, and clean the tip. Make sure the toothed ABS ring is clean too.

QuoteFerdinand
The gap between the tip of the magnet and the toothed ring is critical. Because it is a magnet, it tends to collect bits of "stuff" on it's tip. Undo the bolt holding the sensor, pull it out, and clean the tip. Make sure the toothed ABS ring is clean too.

i think this is why my ABS is messed up after the 5-lug swap. it works, but the brake pedal vibrates against my foot and makes a farting noise every time i come to a stop.

Soldering the relay will make it function, but it will put your computer at risk if there is a voltage spike. Check your wires to the sensors like Ferd said and if everything checks out then you might want to swap in a different computer.

QuoteFerdinand
The gap between the tip of the magnet and the toothed ring is critical. Because it is a magnet, it tends to collect bits of "stuff" on it's tip. Undo the bolt holding the sensor, pull it out, and clean the tip. Make sure the toothed ABS ring is clean too.

Any idea what the critical gap distance is? I suppose if they are all currently the same distance apart, I'll assume they are okay, otherwise I'll move them in to the distance of the closest sensor.

I checked all 4 wheel sensors at their plugs (fyi the rear plugs are located under the rear seat), and found that ever sensor had exactly 1000ohms of resistance. This doesn't strike me as "low" resistance, but it's certainly not high, and they all were exactly the same, so I'm inclined to think this is within spec?